The present invention relates to a sensor for detecting force or acceleration, and relates particularly to a capacitance sensor for detecting force or acceleration in a particular axial direction in an XYZ three-dimensional coordinate system using a capacitance element.
Force sensors and acceleration sensors are used in numerous industrial devices as a means of detecting a particular physical quantity, and as an input device for use with digital devices. Sensors using capacitance elements (capacitance sensors) in particular are used as a low cost data capturing and input device for use with computer devices because of their simple construction and ability to reduce cost.
Capacitance sensors for detecting force or acceleration use a capacitance element of which the electrode gap is changed by the force or acceleration being detected, and detect the desired force or acceleration based on the change in the capacitance of this element. More recent sensors of this type use a plurality of capacitance elements arrayed at specific locations to separately detect a desired two-dimensional or three-dimensional force or acceleration component. U.S. Pat. No. 5,406,848 and U.S. Pat. No. 5,421,213, for example, teach the basic principle of a multi-dimensional capacitance sensor for detecting force, acceleration, or magnetism.
A problem with the various capacitance sensors of the related art is, however, that interference between different detection axes occurs when detecting force or acceleration along a specific detection axis. A multi-dimensional capacitance sensor typically has a dedicated capacitance element along each detection axis with each said element independently outputting a detection value. During actual sensor operation, however, the detected value is affected slightly by the action of the force or acceleration component on an axis other than the intended detection axis of the sensor. This makes it necessary to implement some corrective measure, such as providing a compensation circuit for cancelling the effect of interference between force or acceleration components on different axes. Such measures ultimately complicate the overall structure of the device, and increase production cost.
The object of the present invention is therefore to provide a sensor using capacitance element for obtaining by means of a simple construction an accurate detection value with no interference from another detection axis.
(1) The first feature of the present invention resides in a capacitance sensor using a capacitance element for detecting force or acceleration in a specific axis direction in an XYZ three-dimensional coordinate system having an X-axis, a Y-axis and a Z-axis, comprising:
a bottom fixed layer and a top fixed layer fixed with a specific gap therebetween and with surfaces thereof parallel to an XY plane and intersected by the Z-axis;
a displacement layer disposed between the bottom fixed layer and the top fixed layer so as to maintain a reference state substantially parallel to the XY plane under conditions in which a force or an acceleration is not at work, and to displace from the reference state when a force or an acceleration is at work;
a working body connected to a part of the displacement layer for causing displacement of the displacement layer based on an action of force or acceleration;
a positive X-axis bottom electrode formed on a top surface of the bottom fixed layer at a position corresponding to a positive region of the X-axis;
a negative X-axis bottom electrode formed on a top surface of the bottom fixed layer at a position corresponding to a negative region of the X-axis;
a positive X-axis top electrode formed on a bottom surface of the top fixed layer at a position corresponding to the positive region of the X-axis;
a negative X-axis top electrode formed on a bottom surface of the top fixed layer at a position corresponding to the negative region of the X-axis;
a displacement electrode formed on a bottom surface of the displacement layer at a position corresponding to the positive X-axis bottom electrode;
a displacement electrode formed on a bottom surface of the displacement layer at a position corresponding to the negative X-axis bottom electrode;
a displacement electrode formed on a top surface of the displacement layer at a position corresponding to the positive X-axis top electrode; and
a displacement electrode formed on a top surface of the displacement layer at a position corresponding to the negative X-axis top electrode;
where a positive X-axis bottom capacitance element is formed by the positive X-axis bottom electrode and an opposing displacement electrode;
a negative X-axis bottom capacitance element is formed by the negative X-axis bottom electrode and an opposing displacement electrode;
a positive X-axis top capacitance element is formed by the positive X-axis top electrode and an opposing displacement electrode;
a negative X-axis top capacitance element is formed by the negative X-axis top electrode and an opposing displacement electrode; and
a detection means having a function for detecting a force or an acceleration acting in an X-axis direction based on a difference between
a sum of a capacitance of the positive X-axis bottom capacitance element and a capacitance of the negative X-axis top capacitance element, and
a sum of a capacitance of the negative X-axis bottom capacitance element and a capacitance of the positive X-axis top capacitance element.
(2) The second feature of the present invention resides in a capacitance sensor described in the first feature, further comprising:
a positive Y-axis bottom electrode formed on a top surface of the bottom fixed layer at a position corresponding to a positive region of the Y-axis;
a negative Y-axis bottom electrode formed on a top surface of the bottom fixed layer at a position corresponding to a negative region of the Y-axis;
a positive Y-axis top electrode formed on a bottom surface of the top fixed layer at a position corresponding to the positive region of the Y-axis;
a negative Y-axis top electrode formed on a bottom surface of the top fixed layer at a position corresponding to the negative region of the Y-axis;
a displacement electrode formed on a bottom surface of the displacement layer at a position corresponding to the positive Y-axis bottom electrode;
a displacement electrode formed on a bottom surface of the displacement layer at a position corresponding to the negative Y-axis bottom electrode;
a displacement electrode formed on a top surface of the displacement layer at a position corresponding to the positive Y-axis top electrode; and
a displacement electrode formed on a top surface of the displacement layer at a position corresponding to the negative Y-axis top electrode;
where a positive Y-axis bottom capacitance element is formed by the positive Y-axis bottom electrode and an opposing displacement electrode;
a negative Y-axis bottom capacitance element is formed by the negative Y-axis bottom electrode and an opposing displacement electrode;
a positive Y-axis top capacitance element is formed by the positive Y-axis top electrode and an opposing displacement electrode; and
a negative Y-axis top capacitance element is formed by the negative Y-axis top electrode and an opposing displacement electrode; and
the detection means has a further function for detecting a force or an acceleration acting in a Y-axis direction based on a difference between
a sum of a capacitance of the positive Y-axis bottom capacitance element and a capacitance of the negative Y-axis top capacitance element, and
a sum of a capacitance of the negative Y-axis bottom capacitance element and a capacitance of the positive Y-axis top capacitance element.
(3) The third feature of the present invention resides in a capacitance sensor described in the first or second feature, wherein the bottom electrodes and the top electrodes are symmetrical to the XZ plane or YZ plane.
(4) The fourth feature of the present invention resides in a capacitance sensor described in the third feature, where the capacitance elements are all electrode pairs having the same shape, same size, and same electrode gap.
(5) The fifth feature of the present invention resides in a capacitance sensor described in the first to fourth feature, further comprising:
a bottom origin-surrounding electrode formed around a point of origin on a top surface of the bottom fixed layer;
a top origin-surrounding electrode formed around a point of origin on a bottom surface of the top fixed layer;
a displacement electrode formed on a bottom surface of the displacement layer at a position opposing the bottom origin-surrounding electrode; and
a displacement electrode formed on a top surface of the displacement layer at a position opposing the top origin-surrounding electrode;
where a bottom origin-surrounding capacitance element is formed by the bottom origin-surrounding electrode and an opposing displacement electrode, and
a top origin-surrounding capacitance element is formed by the top origin-surrounding electrode and an opposing displacement electrode; and
the detection means has a further function for detecting force or acceleration acting in the Z-axis direction based on a difference between a capacitance of the bottom origin-surrounding capacitance element and a capacitance of the top origin-surrounding capacitance element.
(6) The sixth feature of the present invention resides in a capacitance sensor described in the fifth feature, wherein the bottom origin-surrounding electrode and the top origin-surrounding electrode are rotationally symmetrical to the Z-axis.
(7) The seventh feature of the present invention resides in a capacitance sensor described in the sixth feature, wherein the origin-surrounding capacitance elements are electrode pairs having the same shape, same size, and same electrode gap.
(8) The eighth feature of the present invention resides in a capacitance sensor described in the first to seventh feature, wherein a first part of the displacement layer is affixed to the bottom fixed layer and top fixed layer,
a second part of the displacement layer is connected to the working body,
a third part of the displacement layer located between the first part and second part is made of a flexible material such that displacement of the displacement layer occurs with deflection of the third part.
(9) The ninth feature of the present invention resides in a capacitance sensor described in the first to eighth feature, wherein a plurality of displacement electrodes formed on the displacement layer are comprised of a single physical common electrode.
(10) The tenth feature of the present invention resides in a capacitance sensor described in the ninth feature, wherein a flexible, conductive substrate is used as the displacement layer, and the displacement layer itself is used as the single common electrode.
(11) The eleventh feature of the present invention resides in a capacitance sensor described in the ninth or tenth feature, wherein the non-common electrodes of each capacitance element pair for which it is necessary to obtain a sum of capacitance values are electrically connected to each other at a connection node, and a capacitance between the connection node and the common electrode is used as the sum.
(12) The twelfth feature of the present invention resides in a capacitance sensor described in the eleventh feature, wherein a through-hole is formed in the bottom fixed layer and the top fixed layer at each electrode forming position to be connected, and a pair of electrodes to be connected is connected using a wiring layer by way of the through-hole.
(13) The thirteenth feature of the present invention resides in a capacitance sensor described in the first to twelfth feature, wherein a perimeter of the bottom fixed layer and a perimeter of the top fixed layer are fastened by a pedestal, a perimeter of the displacement layer is fastened by the pedestal, the working body is connected to a top center part of the displacement layer, and a through-hole for passing through the working body is formed in a center part of the top fixed layer.